1. Field of the Invention
The present invention relates to a rubber track, and, particularly, to a rubber composition for a guide lug material projecting from the inner surface of a rubber track.
2. Description of the Related Art
A rubber track is generally provided with a plurality of guide lugs formed at spaced intervals in the longitudinal direction of the inner surface thereof. In this positive drive type of rubber track, the guide lugs have functions of transferring the driving force from a sprocket and/or preventing the rubber track from slipping off a wheel, which is called "detracking".
It is considered that detracking occurs as follows: The rubber track is hit by a lateral force which produces a relative shift between the rubber track and the wheel. In this case, the guide lug repeatedly contacts and collides with the wheel, while the shifted guide lug is forced to return to its previous, regular position, resulting in abrasion of or damage to the guide lug. There is also a possibility of the detracking.
FIG. 1 shows a rubber track 1, from the inner surface of which a row of guide lugs 3 project. A wheel 5 normally rotates so that it strides over the guide lug 3. When a relative shift between the rubber track 1 and the wheel 5 is produced, the wheel 5, as shown by the dotted line in the figure (only one of the wheels 5 is shown), repeatedly contacts and collides with the guide lug 3 whereby the shift between both is limited and the shifted rubber track 1 is forced to return to its previous, regular rolling contact surface. The abrasion of or damage to both sides of the guide lug 3 is therefore significant.
Furthermore, when the guide lug is engaged with a sprocket, not shown, to convey driving force, a guide lug is always rubbed against a sprocket pin. The guide lug is deformed by the force applied especially to the root, which creates abrasion or damage easily. In addition, the contact and collision between the wheel 5 and the guide lug cause a large running resistance resulting in large energy losses.
In order to solve the aforementioned problem, for instance, Japanese Patent Application Laid-Open (JP-A) No. 6-72362 discloses a structure in which a guide lug projecting from the inner surface of a rubber track is formed with a low friction material exposed to the contact face with the other material. FIG. 3 shows a plate-like low friction material (Ultra High Molecular weight Polyethylene: UHMW-PE) 6 embedded inwardly into the guide lug 3 projecting from the inner surface of the rubber track. As shown in FIG. 3, the low friction material 6 is exposed from both sides 3.sub.3 and the top 3.sub.2 of the guide lug 3 so that it contacts and collides with the wheel 5 and with an idler and a sprocket which are not shown. The friction between the low friction material 6 and these materials is low due to the low friction characteristics of the low friction material 6. This reduces the occurrence of the detracking and the abrasion or damege of guide lugs. And the low running resistance and low energy losses can be obtained due to the good self-lublicating characteristics of this material.
Such a structure using the low friction material 6 poses the following problem: When a relative shift between the guide lug 3 and the wheel 5 is produced, excess force is applied to the guide lug 3. Consequently, the side 3.sub.3 of the guide lug 3 contacts and collides with the wheel 5. At this time, a concentrated stress which is imposed on the boundary between a rubber member of the guide lug 3 and the low friction material 6, though it depends upon the difference in hardness between them, causes breakdown of the boundary. This structure also requires stable adhesion of the low friction material 6 to the rubber member of the guide lug 3.